usb: usbtest: disable dynamic ID support

commit 00e2071f6d upstream.

The usbtest driver relies on the driver_info field of struct usb_device_id
to point to a valid struct usbtest_info descriptor. This structure contains
essential test configurations, such as endpoint addresses and test modes,
which are required during probe.

When a user dynamically adds a new device ID via the sysfs new_id
interface without specifying a reference device, the USB core initializes
driver_info to 0 (NULL). When a matching device is subsequently probed,
usbtest_probe() unconditionally casts driver_info to a struct usbtest_info
pointer and dereferences it, leading to a NULL pointer dereference crash:

  Oops: general protection fault, probably for non-canonical address
  0xdffffc0000000001: 0000 [#1] SMP KASAN NOPTI
  KASAN: null-ptr-deref in range [0x0000000000000008-0x000000000000000f]
  RIP: 0010:usbtest_probe+0x3b9/0x1280 drivers/usb/misc/usbtest.c:2822

Because usbtest strictly requires pre-defined usbtest_info descriptors
to function, dynamic ID binding via sysfs is fundamentally unsupported
for this driver.

Fix this by setting .no_dynamic_id = 1 on usbtest_driver. This instructs
the USB core to skip creating the new_id and remove_id sysfs interfaces
for usbtest, preventing invalid dynamic ID entries from being created.

Cc: stable@vger.kernel.org
Reported-by: syzbot+7e1e5911f9eac50bedc7@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=7e1e5911f9eac50bedc7
Signed-off-by: Aleksandr Nogikh <nogikh@google.com>
Tested-by: syzbot@syzkaller.appspotmail.com
Link: https://patch.msgid.link/20260806152651.2370795-1-nogikh@google.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/misc/usbtest.c

@@ -3053,6 +3053,7 @@ static struct usb_driver usbtest_driver = {
 	.disconnect =	usbtest_disconnect,
 	.suspend =	usbtest_suspend,
 	.resume =	usbtest_resume,
+	.no_dynamic_id = 1,
 };
 
 /*-------------------------------------------------------------------------*/